The main concept of Base 18 is to use modern components (without compromising human-friendly solderability), and that is in the core of its 3.3V logic main bus. There are still number of old parts out there that work on 5V bus only. I want to connect the two worlds and that's why I designed this 3V-5V interface plugin. It converts the B18 bus to 5V levels along with bus supply of 5V, instead of the original 3.3V.
A B18 card in standard format can now connect on top just like any normal card. This one is solderable by hand but requires a bit more skill since the level shifters are SOP 0.65mm pitch, and in addition to that - there is another header to be soldered on the bottom side of the PCB. The passive components are still 1206 size, though.
I am making prototype PCBs and will be posting further updates in due course.